1. Description of the Related Art
This invention relates to an automatic welding machine path correction method for performing welding while weaving a welding torch left and right with respect to a welding line.
2. Background Art
An automatic welding machine performs welding by impressing a voltage across a wire and a workpiece to produce an arc at the tip of the wire, and moving the wire tip along a welding path while the wire is successively paid out in small increments.
FIG. 6 is a schematic view of such a welding machine. In the Figure, WR denotes the wire, which is paid out in small increments in the direction of the arrow by feed rollers FR so that its tip protrudes from the end of a torch TC via an energizing tip ET, with the amount by which the wire is fed being limited in such a manner that the tip comes to occupy a position spaced a predetermined distance from the surface of the workpiece WK at all times. A welding power supply PS, which is for impressing the voltage across the wire WR and the workpiece WK, generates a continuous high voltage at a predetermined period. The plus side of the welding power supply PS is applied to the wire WR through the guide member GB, and the minus side is connected to the workpiece WK. In the torch TC, a shielding gas is supplied by a gas supply source, not shown. By being jetted toward the portion being welded, the shielding gas makes it possible to prevent oxidation of the welded portion of the workpiece WK when welding is carried out.
The high voltage is generated continuously by the welding power supply PS while the shielding gas is fed from the gas supply unit, not shown, and the wire WR is paid out in small increments in the welding machine having the above construction. As a result, an arc is produced at the tip of the wire and both the wire and the portion being welded are melted to weld the fused portions of the workpiece together. It has recently become possible to perform such a welding operation automatically by robot. Specifically, the torch TC of the welding machine is grasped by a robot, which is caused to move the torch (the tip of the wire) along a welding path to weld the workpiece.
When weaving is performed to the left and right of a cutting line CT, as shown in FIG. 4, the robot control unit calculates the extreme points to the left and right from starting and end points, which have been taught, as well as amplitude and frequency. Movement of the torch TC is controlled based on the results of calculation. However, in cases where there are differences in the machined precision of the workpiece or where there is a shift in the attached position, welding cannot be performed accurately at the predetermined location of the workpiece WK even when the robot is controlled based on the taught points to move the torch TC.
Accordingly, as shown in FIG. 5, the conventional practice is to monitor the value of the integral of the welding current and effect a path correction upon comparing the difference between an integrated value prevailing at a leftward swing and an integrated value prevailing at a rightward swing in one cycle of weaving, which corresponds to P.sub.a through P.sub.b in FIG. 4, with a stipulated value, and comparing the integrated value with a reference value when the aforesaid difference exceeds the stipulated value.
With this conventional method of correcting the path based on the integrated value of the welding current, the amount of correction is decided depending on how the stipulated value is chosen. Consequently, in order to actually obtain an optimum amount of correction, it is necessary to perform trials repeatedly upon changing the stipulated value in various ways. That is, when the amount of correction is too large, welding deviates from the welding path and the actual welding line meanders. Conversely, when the amount of correction is too small, welding cannot follow up changes in the shape of the workpiece.